There are available hand-held encoded symbol readers which have an image sensor such as a charge-coupled device (CCD) for reading and decoding two dimensional encoded symbols such as bar codes or tessellated pattern codes having a grid-like pattern of white and black areas, where the pattern changes in both the horizontal (X-axis) and vertical (Y-axis) directions.
One general hand-held encoded symbol reader has a casing with an opening defined at one end which is covered with a transparent plastic panel. The casing houses therein a CCD image sensor facing the opening and electrically connected to a signal processor, a plurality of light-emitting diodes (LEDs), and a condensing lens positioned in front of a photodetector surface of the CCD. Light is emitted from the LEDs and applied through the opening to a two-dimensional encoded symbol such as a bar code that is to be read by the encoded symbol reader. The light is reflected by the encoded symbol back into the opening, and focused by the condensing lens onto the photodetector surface of the CCD. The CCD converts the applied light into image signals, which are then converted by the signal processor into a digital signal. The digital signal then decoded, and the original alphanumeric information can be retrieved.
When the encoded symbol is read by the encoded symbol reader, the entire encoded symbol has to be positioned within the readable range of the CCD because the encoded symbol has pattern that varies in the horizontal and vertical directs as described above. Therefore, it is necessary to properly position the encoded symbol reader with respect to the encoded symbol.
Conventionally, the only way to confirm whether the encoded symbol has been properly positioned within the readable range of the CCD has been to check if the encoded symbol has been properly decoded. Specifically, the operator can recognize that the encoded symbol has been properly positioned within the readable range of the CCD only after the alphanumeric information decoded from the encoded symbol is displayed or successful decoding is audibly indicated.
Therefore, the operator has to move the encoded symbol reader over the encoded symbol, wait to see whether the encoded symbol is properly decoded, and then reposition the encoded symbol reader until the encoded symbol is properly decoded. This can be a time-consuming and tedious process and leads to a loss in efficiency when using the encoded symbol reader.